Method of producing bessemer steel



Patented Nov. 7, 1950 UNITED STATES PATENT oiFfF l-C-E METHOD OF PRUIfZiifi-BESSEMER STEEL .-'1-.ure Robert .Haglund, Stockholm, Sweden, as- .signor to Stora Kopparberjgs -Bergslags Aktiebolag, Falun, Sweden N Drawing. -Appli'cation August 8, 194:7, Serial No. 767,657. In Sweden July 12, 1-943 Section L'PubIic LaW 690.,. A ugus't s, 1946 Patent expires July '12, 1963 .1 i V v The present invention refers to the production of steel or ironaccording to the Bessemer-process "both according to-the acid and according "to the basic method, and the invention has for its object to provide for better facilities for the control of the furnace process and for Obtaining a higher quality product. "The invention is substantially distinguished by the feature that a mixture oi oxygen gas or air enriched in oxygen and carbon dioxide is used as an oxidation gas during the later part of the blowing operation. The carbon dioxide participates "itself in the oxidation process with the formation of CO, heat being then also absorbed. Bessemer-blowing with the use of pure oxygen gas as the oxidation gas produces a reaction so intensive and so great a rise of the temperature 'in the bath that the process becomes 'd'iiilcult to manage. 'By the supply of CO2 to the oxygen gas, heat is absorbed partly through decomposition of C02 and partly by heating of the quantity "of gas, which is increased as compared with the conditions "prevailing when oxygen gas alone is employed. By controlling the quantity of CO2 supplied it will therefore be possible to regulate the temperature conditions during the blowing operation as desired. By the supply of CO2 to the oxygen gas used as an oxidation gas it will thus be possible to conduct the process in such manner that a lesser, a greater or the same heat absorption is obtained, as desired, than with the use of ordinary air, in spite of the fact that the total escapingquantity of gas will be considerably smaller. 1

By Bessemer-blowing by means of a mixture of O2 and CO2 poor in nitrogen a steel or iron will be obtained which is considerably poorer in nitrogen than the product obtained with the use of air. It is not necessary, however, for this purpose to use said gas mixture during the whole of the blowing period. It is suitable to carry out the first and even the substantial portion of the blowing operation with the use of air, the final blowing "being then carried out with a mixture of O2 and CO2 which is poor in nitrogen. A portion of the initially absorbed nitrogen will then escape from the steel or iron during this final blowing period. In the manufacture of iron which is poor in carbon, it is possible, for instance, to blow with air, until the percentage of carbon has been lowered to about 0.5-0-.4%, after which one may pass over to the use of a mixture of oxygen gas and carbon dioxide. If great importance is attached to a low percentage of nitrogen, the change should take place earlier.

volume.

'5 Glaim's. (Cl. {S

It, When using a mixture of an enriched inoxygen together with CO2 as an oxidation gas or iron ne should therefore, in carrying out- Bessemer-blowing with the use of air enriched in oxygen or of a mixture of such an and C62, effect the final blowing with a mixture of O2 and CO2 which is poor in nitrogen.

with the use of a mixture of oxygen gas and carbon dioxide the escaping quantity of gas will be considerably less than when blowing with ordinary air. With the use of an unaltered blowin time the losses by boiling out will therefore be considerably less. it is also possible to carry out the process in such manner that more oxidation agents are supplied per unit of time, whereby the blowing time is out down. In such cases where a low percentage of nitrogen is desired in the product, it is important to blow with a gas mixture having a low percentage of nitrogen, preferably below 4 per cent by For practical reasons the use of pure oxygen gas is not considered economical. On the other hand, it is advantageous to use oxygen gas containing about 96 to '98 Oz. The carbon dioxide may be advantageously obtained from blast furnace gas or from waste gases. The waste gases from the Bessemer converter may also be used for this purpose. v

The percentage of CO2 in the oxidation gas may be varied Within very wide limits. With the use of oxygen gas or of air highly enriched in oxygen it may thus be found suitable to supply so much C92 that the percentage by volume of CO2 amounts to between 40 and In other cases one may use considerably more, for instance up to about in others considerably less, for instance down to 20-30%. In the supply of CO2 to air enriched in oxygen and having a high per centage of nitrogen, smaller quantities counted j the part of the phosphorus above 1.4% P as "a rule oxidizes during the first period of the blow ing operation before or at the same time as the carbon content of the pig iron oxidizes. An

"essential part of the phosphorus content nowthan 1.4%, almost the whole original phosphorus content of the pig iron is still left in the metalbath. The percentage of phosphorusleftin"the iron, when the carbon content is mainly oxidized,

varies to a certain extent depending 'on the rem-=1 perature of the metal duringthe blowing-opera-' tion. At the continuation of the blowing operation, when the final oxidation of the phosphorus takes place, the oxygen content of the blas t-.w;ill

be nearly substantially consumed 0 t Q iQIIIlZ, tion of oxides of phosphorus and iron"whereb no essential formation of carbon monoxidemake 's' When utilizing a blast solely consisting.

place. of air the oxygen will ice almost fully absorbed without formation thereby of other gases. The remainingv part of the blast flowing} through the metal bath will in such case consist almost entirely of nitrogen. Such-;will also be the case when using, a blast consisting solelyof airenriched in oxygen. Thepartial pressure of the nitrogen," when using a blast consisting solely of Qair'or air enriched. inoxygen, will accordingly be considerably increasedduring the operation for thermal oxidation of the phosphorus content, and accordingly. the conditions favoring absorption of-nitrogen in the iron bath considerably increases. h

By utilizing, according to the presentinvention, a blast, containing. air enriched in oxygen and'carbon dioxide duringthe final oxidation of the phosphorus, the partial pressure of the nitrogenj will be considerably reduced and thus the possibilities for the iron bath to absorb nitrogen will be considerably reduced. During the final oxidation of thephosphorus content it .is suit- 'able to adjust the mutual relation between the said oxidizing gases so, that the reaction gaseous products deriving" from the CO2 content of the blast are the main part of the total amount of i gases leaving the metal bath during the said final oxidation. During the oxidation of phosphorus and iron by means ofthe CO2 thesame' Volume of CO is formed as the volume of CO2 consumed for the formation of oxides of phosphorus and iron. The nitrogen derived from the airenrichecl in oxygen will thus be diluted by the aforesaid amount of carbon monoxide and also by the part of the CO2, which occasionaly'does not take part in the reaction. The utilization of ablast consisting only of CO2 for the final oxidation of the phosphorus would of course further reduce the partial pressure of the nitrogen. This way is, however, not practical as the temperature of the iron bath in such case would be decreased more than is desirable.

During the first blowing period, at which the carbon as wen as the part of the phosphorus above about 1.4% P'is oxidized the use of 'a'bla's't of ordinary air is preferable. riched in oxygen.togetherlwithCOZ is, however, according to the invention, usedfor the final oxidation of the phosphorus content. The use of the latter blastcan be'started. immediately afterrthe-carbon content is mainly oxidized, but alternatively the change canbe startedsomewhat earlier, whema part of the carbon, for instance about 0.5% C, is left in the bath or somewhat later i. e after a part of the final. oxidation of ile-1. 9 z F r. inst nc w en the .Prcon- A. blast of air en' 4 tent of the bath has gone down to about 1%. During the first part of the final oxidation of the phosphorus it is sometimes suitable to start with a blast containing air enriched oxygen to a lower degree and also contain mg a lower percentage'of CO2, and then successively or periodically to lower the content of nitrogen and to increase "the percentage of CO2 in the blast. When utilizing. air high1 y enriched in oxygen, for instance containing 90-98% Q2, for composing the CO2 containing blast, this can for instance be done in such' a wayfthat; when changing, the CO2 con- "taining blast at first is blown in together with air,

whereafterthe amount of air is successively or gradually reduced. The proportion CO2ZN2 will hus, increase, as the content of phosphorus in th ironilbath decreases. I It is suitable to adjust "thep'roportion COzINz in such a way, that the content of CO2 counted in volume, at least during the later periodof thefi'final oxidation of phosphorus, ;amounts to 5 to 10 times the'content of nitrogen When utilizingan air enriched with oxygen up to about 90-98% 02 for the final oxidationof the phosphorus, it is suitable to add-such a quantity of. CO that the percentage-of C O2, counted in volume, amounts to, between 20 -40%.

WhatIclaim is: v

1 In the. processior the manufacture of iron or steel from pig iron by Bessemer. blowing con,- sisting in blowingafter the carbon content of the pig iron is reducedto, about 0.5% witha, blast essentially consisting byvolumeof at least 20% carbon dioxide, at least20 oxygen and less-than 10 nitrogen'with the carbon dioxide and oxygen forming at least 90% of said blast. 53 2. In the processfor the manufacture of iron orsteel from pig ironby Bessemer blowingeoonisisting in blowing after the carbon'content ofthe pig iron is reduced to' about 0.5% with a blast essentially consisting by volume of at least 20% oxygen, 20% to carbon dioxide and ;;less that 4% nitrogen with the carbon dioxide and oxygen forming atleast .90% of. said blast,-.-

3. In the process for the manufacture of iron or steel from pigiron by Bessemer --.blowing consisting in blowing; with a blast essentially con;- sisting of air until the carbon content of the bath is lower than 0.5% and the blowing with. a blast essentially consisting by volume ofat least 20% carbon dioxide, at least 20% oxygen. and..-less than 4% nitrogen withthecarbon dioxide and oxygen forming at least 910% of said-blast.

4; In-the process for the manufacture of iron or steel from pig iron by Bessemer blowing consisting in blowing with a blast essentially consisting of air during the oxidizing of a substantial portion of the carbon content of the pig-iron, and thereafter blowing with. a blast essentially consisting by volume of atleast 20 carbon dioxide, at least 20% oxygenand less than. 10% nitrogen with the carbon dioxide and oxygen forming at least of said blast. v I

5:: In the process for the manufacture of iron or steel from pigiron richin phosphorus by basic Bessemer. blowing consisting in blowing witha blast essentially consisting of air until the. carbon content ofthe-bath is lower than 0.1% and the blowing with ablast essentially-,consisting by volume of .at least 20% carbon dioxide, at least 20% oxygen andless than 4% nitrogen withthe carbon dioxideand oxygen forming at least 90% of saidblast. 5

- TURE ROBERT HAGLUND.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 75,240 Bennett Mar. 10, 1868 86,859 Phillips Feb. 9, 1869 843,592 Eldred Feb. 12, 1907 1,034,785 Greene Aug. 6, 1912 1,608,270 Friderich Nov. 23, 1926 1,709,389 Davis Apr. 16, 1929 2,077,568 Kinzel Apr. 20, 1937 2,333,654 Lellep' Nov. 9, 1943 Number 6 FOREIGN PATENTS Country Date France Sept. 4, 1939 France Apr. 13, 1942 Germany July 17, 1907 Great Britain Feb. 29, 1928 Great Britain Feb. 21, 1940 OTHER REFERENCES 10 Fourth Report on the Heterogeneity of Steel Ingots, published by the British Iron and Steel Institute, London (1932), page 89. 

4. IN THE PROCESS FOR THE MANUFACTURE OF IRON OR STEEL FROM PIG IRON BY BESSEMER BLOWING CONSISTING IN BLOWING WITH A BLAST ESSENTIALLY CONSISTING OF AIR DURING THE OXIDIZING OF A SUBSTANTIAL PORTION OF THE CARBON CONTENT OF THE PIG IRON, AND THEREAFTER BLOWING WITH A BLAST ESSENTIALLY CONSISTING BY VOLUME OF AT LEAST 20% CARBON DIOXIDE, AT LEAST 20% OXYGEN AND LESS THAN 10% NITROGEN WITH THE CARBON DIOXIDE AND OXYGEN FORMING AT LEAST 90% OF SAID BLAST. 